Structure and magnetic properties of RCo9Si2 systems

RCo₉Si₂ alloys (R=Sm, Gd, Tb, and Er) were synthesized and examined by X-ray diffraction and high-field (90 kOe) magnetometry in the temperature range 4.2 to 700 K. X-ray powder diffraction analyses indicated that the major phase crystallizes in the tetragonal BaCd₁₁-type structure. The presence of a small amount of extraneous phase was also detected. The magnetic ordering temperatures were observed to vary between 415 and 483 K in order Er, Tb, Gd, and Sm. This behavior is found to follow the de Gennes function and can therefore be ascribed to the strength of the rare-earth-cobalt exchange interaction. The average Co moment in RCo₉Si₂ was determined to be nearly 0.9 μmB at 4.2 K. All compounds studied showed an increase in magnetization with field, beyond technical saturation in fields up to 90 kOe. The M versus T on SmCo₉Si₂ indicates a spin reorientation transition at about 60 K. This can be attributed to the effect of the competing anisotropies of the Sm and Co sublattices